Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
Many applications require a high level of functional integration, which can be achieved with a package-on-package (PoP). FIG. 1 shows a conventional PoP 10 with semiconductor die 12 mounted to substrate 14 with die attach adhesive 16. Semiconductor die 12 is electrically connected to contact pads 17 formed on substrate 16 with bond wires 18. Bumps 19 are formed on contact pads 17. An encapsulant 20 is deposited over semiconductor die 12 and substrate 16. Bumps 21 are also formed on contact pads 17 formed on an opposite surface of substrate 14. A portion of encapsulant 20 over bumps 19 is removed by a grinding process in order to mount semiconductor die 22. After the grinding operation, semiconductor die 22 can be mounted to encapsulant 20 with bumps 23 electrically connected to bumps 19.
FIG. 2 shows another conventional PoP 24 with semiconductor die 26 mounted to substrate 28 with die attach adhesive 30. Semiconductor die 26 is electrically connected to contact pads 31 formed on substrate 28 with bond wires 32. Bumps 33 are also formed on contact pads 31. An encapsulant 34 is deposited over semiconductor die 26 and substrate 28. Bumps 35 are formed on contact pads 31 formed on an opposite surface of substrate 28. A portion of encapsulant 34 over bumps 33 is removed by an etching process in order to mount semiconductor die 36. After the etching operating, semiconductor die 36 can be mounted to encapsulant 34 with bumps 38 electrically connected to bumps 33. The grinding and etching to make headroom for mounting an upper semiconductor die can induce stress and cause defects in the PoP.